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•The response of Anammox process to Cr(VI) stress were evaluated.•Cr(VI) inhibition mechanism on Anammox was investigated for the first time.•Intracellular Cr(VI) reduction dominated ...with the percentage of 99.78%.•Nitrite oxidation to nitrate was unexpectedly observed.
The toxicity of hexavalent chromium (Cr(VI)) is one of the challenges in implementing Anammox process to ammonium-rich wastewater treatment. However, the response of Anammox process to Cr(VI) stress and the inhibition mechanism remain unclear. Here, two Anammox UASB reactors were operated for 285 days under different Cr(VI) stresses. The results showed Anammox performance was not affected at low Cr(VI) concentration (i.e., 0–0.5 mg L−1), but was severely inhibited at 0.8 mg L−1. Attempts to domesticate Anammox process to higher Cr(VI) by lowering nitrogen loading rate were failed. Examination of Cr(VI) fate showed the occurrence of extracellular and intracellular Cr(VI) reduction to Cr(III). The inhibition was ascribed to the significant intracellular Cr(VI) reduction, accounting for 99.78% of the total Cr(VI) reduction. Moreover, under long-term Cr(VI) exposure, most nitrite was oxidized to nitrate. But microbial community showed no enrichment of Cr(VI) reducing bacteria and other nitrogen transformation-related bacteria.
Palm oil mill effluent (POME) is generated from the sterilization, condensation and hydrocycloning of palm oil in mills. If the effluent is discharged into the aquatic and terrestrial ecosystem ...without treatment, it could lead to high biological oxygen demand (BOD), chemical oxygen demand (COD) and acidic pH of the receiving waters. Biogas consisting mostly of methane, carbon dioxide, and to a lesser hydrogen has been produced through anaerobic treatment of this toxic effluent. The process of biogas production involves microbial synthesis involving hydrolysis, acidogenesis, acetogenesis and methanogenesis. Biogas is formed during anaerobic degradation of POME by indigenous microbial communities. This review updates the current state of art of biogas production through anaerobic digestion of POME using different configurations of reactors such as fluidized bed reactor, anaerobic filtration, up-flow anaerobic sludge blanket (UASB) reactor, anaerobic contact digestion, up-flow anaerobic sludge fixed-film (UASFF) reactor, modified anaerobic baffled bioreactor (MABB), anaerobic baffled bioreactor (ABR), continuous stirred tank reactor (CSTR), expanded granular sludge bed (EGSB) reactor, Ultrasonicated membrane anaerobic system (UMAS), Ultrasonic-assisted Membrane Anaerobic System (UAMAS), membrane anaerobic system (MAS)and upflow anaerobic sludge blanket reactor (UASBR). The factors that influences biogas yield during treatment include pH, temperature (environmental factors), organic loading rate (OLR), hydraulic retention time (HRT), mixing rate, pressure, equilibrium, nutrient and microbial activities (Internal factors). Based on this study, UAMAS is the best configuration for methane production from POME during anaerobic treatment. Biogas from POME could contribute to energy sources of oil palm producing nations, while preventing the attendant environmental impacts associated with its disposal.
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•An innovative fixed-film anaerobic reactor was applied to sugarcane vinasse.•Stable operation was observed for OLRs as high as 30kg COD m−3day−1.•Propionate buildup did not impact ...the stability of the structured-bed reactor.•Enhanced bioenergy recovery was estimated from biodigestion with phase separation.•Energy extraction was over 20% higher compared to single-phase systems.
This study considered the application of anaerobic digestion (AD) with phase separation combined with the use of an anaerobic structured-bed reactor (ASTBR) as the methanogenic phase for the treatment of sugarcane vinasse, a high-strength wastewater resulting from ethanol production. Two combined thermophilic acidogenic-methanogenic systems formed by one single acidogenic reactor followed by two methanogenic reactors operated in parallel were compared, namely, a conventional UASB reactor and an upflow ASTBR reactor. Increasing organic loading rate (OLR) conditions (15–30kgCODm−3d−1) were applied to the methanogenic reactors. The results highlighted the feasibility of applying the ASTBR to vinasse, indicating a global COD removal higher than 80%. The ASTBR exhibited a stable long-term operation (240days), even for OLR values as high as 30kgCODm−3d−1. The application of similar conditions to the UASB reactor indicated severe performance losses, leading to the accumulation of acids for every increase in the OLR. An energetic potential of 181.5MJ for each cubic meter of vinasse was estimated from both hydrogen and methane. The provision of bicarbonate alkalinity proved to be a key factor in obtaining stable performance, offsetting the limitations of relatively low hydraulic retention times (<24h).
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•56% of the energy contained in the agave bagasse was recovered by two-stage process.•Energy recovery from two-stage process was 7 times higher than one-stage process.•The increase of ...stirring speed decreased the H2-consumption by homoacetogenesis.•In the second-stage, methane yields of 90% were obtained at high OLR and short HRT.
Continuous H2 and CH4 production in a two-stage process to increase energy recovery from agave bagasse enzymatic-hydrolysate was studied. In the first stage, the effect of organic loading rate (OLR) and stirring speed on volumetric hydrogen production rate (VHPR) was evaluated in a continuous stirred tank reactor (CSTR); by controlling the homoacetogenesis with the agitation speed and maintaining an OLR of 44 g COD/L-d, it was possible to reach a VHPR of 6 L H2/L-d, equivalent to 1.34 kJ/g bagasse. In the second stage, the effluent from CSTR was used as substrate to feed a UASB reactor for CH4 production. Volumetric methane production rate (VMPR) of 6.4 L CH4/L-d was achieved with a high OLR (20 g COD/L-d) and short hydraulic retention time (HRT, 14 h), producing 225 mL CH4/g-bagasse equivalent to 7.88 kJ/g bagasse. The two-stage continuous process significantly increased energy conversion efficiency (56%) compared to one-stage hydrogen production (8.2%).
•Semi-continuous biological/electrochemical process mineralize organics from slaughterhouse wastewater.•90% of COD decay by anaerobic digestion produces more than 0.35 L Lreactor−1 d−1 of ...methane.•The effluent of UASB was treated by SPEF process reaching almost total mineralization.•The semi-continuous process produces colorless and odorless water.•The combined processes reduce costs for the treatment of slaughterhouse wastewater.
A new semicontinuous anaerobic digestion/solar photoelectro-Fenton (SPEF) process for the treatment of slaughterhouse wastewater is studied. An Upflow Anaerobic Sludge Blanket (UASB) reactor was used at two different organic load rates (OLR) (3.94 and 8.15 g COD L−1 d−1), while the SPEF was carried out in a photoelectrochemical reactor using a filter press cell with a DSA anode and an air diffusion cathode. The results showed that the UASB reactor achieved up to 70% COD removal for the highest OLR, with a low efficiency of suspended solid removal. The anaerobic effluent was treated by the SPEF process, resulting in 88% and 72% COD removal for the initial concentrations of 195 ± 14 mg L−1 and 867 ± 52 mg L−1, respectively, and a turbidity reduction of up to 80%. The treatment of wastewater by SPEF using a current density of 10 mA cm−2 was five times less costly than that of 25 mA cm−2, with an associated cost of 1.4 USD h−1 for the treatment. The proposed semicontinuous processes eliminate at least 91% of the total COD, thus representing a new option for the treatment of slaughterhouse wastewater.
This report demonstrates the fabrication of a composite hollow fiber membrane that efficiently recovers dissolved methane (dCH4) from anaerobic wastewater treatment effluents via membrane contactor ...(MC) process. We first fabricated highly porous hollow fiber membranes (∼85% porosity) using polyvinylidene difluoride (PVDF). Then, we coated the whole structure (bulk), or lumen side of PVDF supports with polydimethylsiloxane (PDMS), a hydrophobic polymer possessing high gas permeability. The adjustment of the concentration of PDMS precursor mix could effectively serve for tuning the performance characteristics of MC membranes and helped suppress membrane wetting, a major performance-reducing factor. Despite their denser skin layers, the lumen-modified membranes demonstrated superior dCH4 recovery flux. Mass transfer analyses have confirmed the importance of preserving bulk porosity while coating the membrane surfaces. The long-term performance tests performed using actual anaerobic effluents suggested that the PDMS coating did not accelerate fouling, such that the lumen-modified MC membranes showed an almost steady flux for 8 days with an anaerobic membrane bioreactor effluent. A high-strength effluent, obtained from an up-flow anaerobic sludge blanket reactor, induced faster fouling. However, we observed only a ∼20% flux decline in a 10-day operation. Thus, we propose that the designed PDMS-PVDF composite membranes are promising for industrial practices.
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•We prepared PDMS-coated PVDF porous hollow fiber membranes for membrane contacting.•Both lumen- and bulk-modified PVDF membranes were successful in methane recovery.•Lumen-modified PDMS-PVDF membrane outperformed commercial PP and PDMS membranes.•Lumen-modified PVDF achieved long-term performance with actual anaerobic effluents.
The present study investigates the technical possibilities of hydrogen and methane production from palm oil mill effluent (POME). The production was carried out in two stage (thermophilic and ...mesophilic) continuous phase with recirculation of the digestate sludge. The reactors used for the present study, up-flow anaerobic sludge blanket reactor (UASB) and continuous stirred tank reactor (CSTR) were operated under thermophilic and mesophilic conditions, respectively. The UASB reactor was operated at 2 days hydraulic retention time (HRT) and 75 kgCOD m3 d−1 organic loading rate (OLR) for hydrogen production. The effluents from UASB reactor containing mainly with acetate and butyrate were directly fed into CSTR for methane production and 5 days HRT was maintained. Both UASB and CSTR reactors were operated for 120 days continuously, and a stable production of the hydrogen and methane was obtained in the separate reactors. The maximum hydrogen and methane production rate achieved was 1.92 L H2 L−d−1 and 3.2 L CH4 L−1 d−1, respectively. The cumulative hydrogen and methane yields were 215 L H2/kgCOD−1 and 320 L CH4/kgCOD−1, respectively with the total COD removal efficiency of 94%. Thermoanaerobacterium species was dominant in hydrogen reactor, while methane reactor was dominated with Methanobrevibacter sp.
•Assessment of hydrogen production potential and methane production potential in batch experiments.•Evaluation of continuous hydrogen and methane production by digestate sludge recirculation without the addition of pH buffers.•Investigation of the polypropylene for the enhancement of methane production at short HRT in CSTR.
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•Biogas upgrading to 82% CH4 is feasible in a thermophilic granular UASB reactor.•H2 is introduced in a separate chamber having a volume of 25% of the reactor.•H2 low gas-liquid mass ...transfer rate limits the availability of H2 for methanogens.•H2 distribution can be improved using porous inert devices, like ceramic sponge.•Gas recirculation and chamber configuration help to maximize CO2 conversion to CH4.
Biological biogas upgrading coupling CO2 with external H2 to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H2 to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO2 in the biogas into CH4, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H2 was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H2 through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO2 content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH4 content.
Hollow fibre membrane contactor (HFMC) systems have been studied for the desorption of dissolved methane from both analogue and real anaerobic effluents to ascertain process boundary conditions for ...separation. When using analogue effluents to establish baseline conditions, up to 98.9% methane removal was demonstrated. Elevated organic concentrations have been previously shown to promote micropore wetting. Consequently, for anaerobic effluent from an upflow anaerobic sludge blanket reactor, which was characterised by a high organic concentration, a nonporous HFMC was selected. Interestingly, mass transfer data from real effluent exceeded that produced with the analogue effluent and was ostensibly due to methane supersaturation of the anaerobic effluent which increased the concentration gradient yielding enhanced mass transfer. However, at high liquid velocities a palpable decline in removal efficiency was noted for the nonporous HFMC which was ascribed to the low permeability of the nonporous polymer provoking membrane controlled mass transfer. For anaerobic effluent from an anaerobic membrane bioreactor (MBR), a microporous HFMC was used as the permeate comprised only a low organic solute concentration. Mass transfer data compared similarly to that of an analogue which suggests that the low organic concentration in anaerobic MBR permeate does not promote pore wetting in microporous HFMC. Importantly, scale-up modelling of the mass transfer data evidenced that whilst dissolved methane is in dilute form, the revenue generated from the recovered methane is sufficient to offset operational and investment costs of a single stage recovery process, however, the economic return is diminished if discharge is to a closed conduit as this requires a multi-stage array to achieve the required dissolved methane consent of 0.14mgl−1.
•Mass transfer analysis of dissolved methane recovery for membrane contactors.•Dissolved methane recovery from UASB configuration is described.•Dissolved methane recovery from anaerobic MBR configuration is described.•Cost estimation undertaken to establish process economic viability.
In this study, the microbial community structure was assessed in an anaerobic ammonium oxidation–upflow anaerobic sludge blanket (ANAMMOX-UASB) reactor treating high-strength wastewater ...(approximately 700 mg N L
−1
in total nitrogen) by employing Illumina high-throughput sequencing analysis. The reactor was started up and reached a steady state in 26 days by seeding mature ANAMMOX granules, and a high nitrogen removal rate (NRR) of 2.96 kg N m
−3
day
−1
was obtained at 13.2∼17.6 °C. Results revealed that the abundance of ANAMMOX bacteria increased during the operation, though it occupied a low proportion in the system. The phylum
Planctomycetes
was only 8.39 % on day 148 and
Candidatus Brocadia
was identified as the dominant ANAMMOX species with a percentage of 2.70 %. The phylum of
Chloroflexi
,
Bacteroidetes
, and
Proteobacteria
constituted a percentage up to 70 % in the community, of which the
Chloroflexi
and
Bacteroidetes
were likely to be related to the sludge granulation. In addition, it was found that heterotrophic denitrifying bacteria of
Denitratisoma
belonging to
Proteobacteria
phylum occupied a large proportion (22.1∼23.58 %), which was likely caused by the bacteria lysis and decay with the internal carbon source production. The SEM images also showed that plenty of other microorganisms existed in the ANAMMOX-UASB reactor.
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